PROBLEMS
- Render times can take up to 3-5 hours
- Exporting (sharing) can take up to 3-5 hours
- In many cases, when I leave to do something else while it is processing, FCPX crashes. So often I need to start render or export over.

QUESTIONS
1) Why do I lose my render files? (And need to start over?)
2) Are there settings I need to use to minimize time of both render and export?
3) What can I do to prevent the FCPX crashes? (These occur both when rendering and export.)
4) Can I bypass render when exporting (sharing)? If yes, does it save me any time?

You're overwhelming your hardware. I would suggest going to proxy mode for editing then when you're completely done switch back to original media mode and export.

Or condense down some of the layers to exports and simplify the number of simultaneous tracks. That many layers would nearly overwhelm a top of the line Mac Pro off the internal SSDs to say nothing of a MBP on an external drive.

I'd agree you're probably just running out of resources on that machine. My only suggestion would be to reboot right before you render and make sure there's as little running in the background as possible other than FCPX.